System for correcting sound records



Patented Apr. 24, 1934 ETE STATES PAT SYSTEM Fort coRitEC'rING SOUNDRECORDS Roy J. Pomeroy, Los Angeles, Calif.

10 Claims.

This invention relates generally to sound recordation and reproduction;and it may be stated as a general object of the invention to providemethods and means for compensating the distcrtions which arise in therecordation and reproduction of sound. This case is a companion to priorapplications entitled System for correcting sound records, Ser. No.279,789, led May 22nd, 1928, Patent No. 1,828,940, issued Oct. 27, 1931,System for correcting sound records, Ser.

No. 279,799, filed May 22, 1928, Patent No.

1,828,941, issued Oct. 27, 1931, and System for correcting soundrecords, Ser. No. 565,571, iiled Sept. 28, 1931. The present inventionmay be considered in the nature of a simplication and improvement on themethods and systems described in said companion cases.

The invention is broadly applicable to any record of sound Waves, but isprobably most conveniently illustrated and described in connection withthe photographic type of record. The particular type of photographicrecord with which I have chosen to illustrate the invention consists ofa shaded band of constant density, a variable outline representing thesound character and volume. It is to be understood, however, that theinvention is not limited to that type of record in any sense, that typeof record having been chosen for typical illustration only.

In recording and reproducing sound, distortions are always introduced byreason of nonlinear characteristics of the various units involved. Inphotographic recording, it is often true that the chief distortions areintroduced in the reproducing system, and particularly by the speakingunit, the distortions of the recording system being relatively small bycomparison, and the chief concern in such cases is therefore With thedistortions of reproduction. v

It is therefore the general object of the present invention to provideimproved and simplied means for compensating the distortions ofrecordation and reproduction, and especially the distortions ofreproduction since in certain cases the distortions of recordation maybe neglected.

The general method involves the making of a distortion corrected record,wherein the distortion characteristic of the system are added to thetrue sound characteristics, but said distortion characteristics areadded in a reverse sense, so that the added distortion characteristicsare compensatory of, or have a neutralizing effect on, the distortionswhich are introduced by the various units of the system. In thepreviously mentioned case, Ser. No. 279,789, thisA is accomplished bywhat may be termed a photographic method, wherein an originalphotographic record is made, and then reproduced as sound. 'Ihedistorted sound thus obtained is then photographically recorded, and anegative of the resulting distortion record is photographically combinedwith a negative record of the original sound to make a correctionrecord, and this correction record is then finally photographicallycombined with an original record to make the distortion correctedrecord. In application Ser. No. 279,790, there is described a methodwhich substituted for the photographic combining of the original anddistortion records, the combining of electrical sound currentsrepresenting said records, Whereby there is obtained a resultantelectrical current representing the differences of said records, or inother Words the distortion alone. A record of this distortion current ismade upon a film, and said record is subsequently printed along with theoriginal record, the result being sound record reversely corrected fordistortion, similar to that obtained by the method rst mentioned. Inapplication Ser. No. 565,571, there is described and is claimed asimplication of the last described method.

The present case is similar to the two cases last mentioned, in thatthere is obtained an electrical current representing the distortionsintroduced by the various units in the system, but instead of making arecord of this distortion representing current, said current is combinedwith a portion of the current representing the original undistortedsound, or representing the sound distorted only by the recording system,and such combination is so el'ected that the distortionrepresentingcurrent is added reversely to the original or undistorted current. Thatis, the distortion representing' current is added to the undistortedcurrent in such a manner that there is 9 obtained a current which isdistorted reversely tothe distortions resulting from passing through thevarious units of the system. This reversely distorted electrical currentis then recorded, thereby producing a reversely distorted sound record.Upon reproduction or" said record, the distorting effects of the systemthen act, as in the previous cases, to bring the sound wave back to itsoriginal form for reproduction.

Reference is now directed to the accompanying drawing, wherein there isshown a simplified system whereby the invention may be practiced, and inWhich:

Fig. 1 is a simplied diagram ofA a circuiting' and recording system inaccordance with the invention;

Fig. 2 shows the original sound current;

Fig. 3 shows the distorted sound current;

Fig. 4 shows the current resulting from diiierentially combining thecurrents of Figs. 2 and 3; and

Fig. 5 shows the sound current obtained by differentially combining thecurrent of Fig. 4 with that of Fig. 2.

In Fig. 1 of the drawing microphone M1 is shown connected by leads 10and 11 to an emplier A1. Amplifier A1 and other amplifiers to bementioned may be any suitable electrical or vacuum tube amplifiersadapted to amplify audiofrequency currents. The output leads 12, 13 ofamplier A1 are connected to a glow tube G1 or other light Varyingdevice. Positioned to beatfected by the light from glow tube G1 is aphotoelectric cell P1, a light slit S1 being shown interposed betweenthe glow tube and cell. Leads 15, 16 from photoelectric cell P1 connectto an amplifier A2, and the output leads 22, 23 of amplii-ler A2 connectto a speaker H.

Microphone M1 picks up the original sound, and an electrical soundcurrent is conducted therefrom by leads 10, l1 to amplifier A1, andafter ampliiication is conducted by leads 12, 13 to glow tube G1. Theelectrical sound current in circuit l2, 13 represents the original soundand is distorted only by the units M1 and A1, and such distortions maybe negligible as compared with other distortions in the system. Lightrays are transmitted from glow tube G1 through slits S1 to aiiectphotoelectric cell P1, and the resulting sound current from thephotoelectric cell is conducted by leads l5, 16 to ampliiier A2, theamplied current passing to speaker I-I and there being reproduced assound. The sound reproduced by speaker H is picked up by microphone M2,a sound current being conducted therefrom to an amplifier A3. The outputleads 20 and 21 of amplier A3 then carry an electric sound current whichis identical with that in output circuit 12, 13 of amplifier A1 exceptfor having imposed thereon the distortions arising in glow tube G1,reproducing system P1, A2 and I-i, and sys-- tem M2, A3. The reproducingsystem P1, A2, l-I, must be one having characteristics identical withthe one to be used in nal reproduction, and the system M2, A3 should beone having characteristics identical with the original system M1, A1, orone introducing little or no distortion. Fig. 2 shows the sound currentwave 40 in the output circuit 12, 13 of amplifier A1, which wave has thedistortions of recording units M1 and A1, and Fig. 3 shows thecorresponding sound current wave 41 in the output circuit 20, 21 ofamplifier A3, the latter wave having, in addition to the recordingdistortions of units M1 and A1, the artificial recording distortions or"glow tube G1 and system M2, A3 and the reproducing distortions of systemP1, A2, I-I. Wave 41 is shown at 41 in Fig. 2, superposed over wave 40,and the last mentioned distortions are represented by the differencebetween said waves.

These electrical sound current waves in circuits 12, 13 and 20, 21 arenow to be diierentially combined, and for this purpose connections suchas leads and 61 may be made between said circuits. Circuits l2, 13 and20, 21 are connected with such regard for polarity that their currentsoppose one another, the resulting current then representing simply theirdifference, or in other words the total distortion of units G1, F1, A2,H,

M2, and A3. Potentiometers 64 and 65 are shown connected in the circuitfor the purpose of so balancing the potentials that the sound currentcomponents can exactly neutralize, leaving simply the differentialdistortion representing current. In series with circuits 60, 61 areleads 62, 63 connecting to the input terminals of an amplier A4. Withthe sound current components neutralized in circuit 66, 61 the resultantdistortion representing current in said circuit may consist of a currentWave such as indicated at 46 in Fig. 4.

There is then in the output circuit 70, 71 of amplifier A, an electricalcurrent wave (an amplication of wave 45) representing the artiiicialrecording and reproducing distortions resulting from glow tube G1,reproducing system P1, A2, H, and system M2, A3; and there is in outputcircuit 12, 13 of ainpliiier A1 an original electrical sound current,indicated at 40 in Fig. 2, distorted only by the recording units M1 andA1. These two currents are now to be differentially combined in such amanner as to produce a resultant sound current distorted reversely tothe directions of the distortions introduced by the above named articialrecording and reproducing units. For this purpose the followingconnections may be made: Leads l2, 13 are shown connected to a controlaniplier A5, although this ainpliiier may not be required since thecurrent in circuit 12, 13 is already in an amplifier state; and, whenused, amplifier A5 merely fullls the function of controlling theamplitude level to match the amplitude level of the current in outputcircuit 70, 7l of amplier A4. The output leads 72, 73 oi varnpliner A5and the output leads 70, 7l of amplifier A4 are shown connected togetherthrough balancing potentiometers 75 and 76 by means of a circuit 7 7,73, and these connections are made with such regard for polarity thatthe distortions are subtracted, so to speak, from the sound currentoutput of amplifier or in other words are added reversely to said soundcurrent.

Thus the connections are so made that the two current waves oppose oneanother, and the result is that the distortion characteristics of thesystern G1, P1, A2, I-I, M2 and A3 are subtracted from the sound currentwave having the distortions of M1 and A1. In Fig. 5 there is indicatedat 40 the outline of the sound current wave output of amplifier A5(which wave corresponds to the wave illustrated in Fig. 2), and at 48the resultant re- Versely distorted sound current wave obtained by theopposed combination of the two current waves in circuit 77, 78. It willbe obvious by comparison with Fig. 4 that the distortions are subtractedfrom, or added reversely to, the sound current wave output of amplierA5. In series with circuit 77 78 carrying the reversely distorted soundcurrent there is shown a glow tube G2, preferably of characteristicsexactly like that of glow tube G1, before which travels an actinic iilm80, a slit S2 being shown interposed between glow tube G2 and film 80.Elements G2 and S2 are conventionally illustrated as typical of anyapproved recording means. Film 8G thus takes a photographic record 82 oithe reversely distorted sound current wave (Fig. 5) oi circuit 77, 78,and this sound record 82 is likewise reversely distorted, as will now befully understood.

It will be remembered that the output current of amplier A1 resultedfrom the differential combination of one current wave distorted byrecording unit M1 and A1, and another current wave distorted byrecording units M1, A1, G1, reproducing units P1, A2, H, and recordingunits M2 and A3, and that said output wave therefore involves thedifference of the two waves,'or in other words the distortions ofreproducing units P1, A2, H, and recording units G1, M2, and A3. Thislast current wave, having the distortions of the last named units, isthen combined in circuits '77, '78 with a current wave having thedistortion of M1 and A1, and the resultant wave is therefore a soundcurrent wherein the distortions of units M1 and A1 are cancelled by thedistortions of units M2 and A3, thus leaving a current wave reverselydistorted by the remaining distortions, i. e., those of recording unitG1 and of reproducing units P1, A2, and H. In making record 82, thereverse distortions of G1, whatever they may be, are cancelled inpassing through G2, and record 82 is therefore reversely distorted byreproducing system P1, A2 and H, all other distortions having beencancelled. Upon any subsequent reproduction of record 82 by a systemhaving distortion characteristics like those of system P1, A2, and H,those characteristics will then act to correct the Waves resulting fromthe reversely distorted record by exact cancellation of the remainingreversely introduced distortions, thereby bringing the wave shape backtoits original form for audible reproduction.

It may here be mentioned that in case of an appreciable time lagintroduced in the artificial reproducing and recording systems, acorresponding time lag may be introduced to the sound current in circuit12, 13 between the glow tube leads and the balance of the system by theuse of usual 1 transmission line pads. Such provisions are wellunderstood in the art and are therefore not illustrated.

While I have now illustrated and described certain specific means forcarrying out an embodiment of my invention, it will be obvious thatvarious changes in design, structure and system arrangement may beeffected without departing from the spirit and scope of my invention;and it is therefore to be understood that all such .changes arecontemplated within the scope of my invention as expressed in thefollowing claims.

I claim:

l. The method of making corrected sound records, that includes producinga substantially une' 3 `distorted original electrical sound current ofthe 'original sound, audibly reproducing sound therefrom, such soundhaving the distortions of reproduction, producing an electrical soundcurrent from the distorted sound, differentially comr .bining said lastmentioned sound current with a 'portion of the substantially undistortedsound current in such a manner that the sound currents are neutralizedexcept for a distortion-representing current, combining thedistortion-represent- `ing current with a portion of the original soundvcurrent in such a manner as to obtain a sound current reverselydistorted to the distortions of reproduction, and making a sound recordfrom said reversely distorted sound current.

2. 'Ihe method of making sound records, that vincludes producing anoriginal electrical sound current from the original sound, audiblyreproducing sound from a portion of said original sound current, suchsound having distortions of reproductions, producing an electrical soundcurrent from said distorted sound, differentially combining said lastmentioned sound current with a portion of the original sound in such amanner that the sound currents are neutralized except for adistortion-representing current, combining said distortion representingcurrent, with a portion of the original sound current in such a manneras to obtain a sound current reversely distorted to the distortions ofreproduction, and making a sound record from said reversely distortedsound current.

3. The method of making sound records, that includes producing anoriginal electrical sound current from the original sound, audiblyreproducing sound from a branch of said original sound current, suchsound having distortions of reproduction, producing an electrical soundcurrent from said distorted sound, differentially combining said lastmentioned sound current with another branch of the original sound insuch a manner that the sound currents are neutralized except for adistortion-representing current, combining said distortion representingcurrent with another branch of the original sound current in such amanner as to obtain a sound current reversely distorted to thedistortions of reproduction, and making a sound record from saidreversely distorted sound current.

4. The method of making sound records, that includes producing anoriginal electrical sound current from the original sound, such currenthaving the distortions of its production from sound, audibly reproducingsound from a portion of said original sound currents, said soundcurrents having said above mentioned distortions and the totaldistortions of reproduction, producing an electrical sound current fromsaid last mentioned sound current, said sound current having in additionto the distortion of the reproduced sound the distortion of itsproduction from the distorted sound, differently combining said lastmentioned sound current with a portion of the original sound current soas to obtain a resultant current representing the distortion ofreproduction oppositely, combining said last mentioned current with aportion of the original sound current so as to obtain a resultant soundcurrent reversely distorted by said distortions of reproduction, andmaking a record of said resultant sound current.

5. The method of making corrected sound records, that includes producingan electrical sound current from the original sound, producing from aportion of said sound current an electrical current representingdistortions of reproduction, oppositely combining said distortionrepresenting current with another portion of said original sound currentso as to obtain a differential sound current distorted reversely by theamount of said distortions, and recording said last mentioned current.

6. The method of making corrected sound records, that includes producingan electrical sound current from the original sound, producing from aportion of said sound current an electrical ourrent representingdistortions of recording and reproduction, oppositely combining saiddistortion representing current with another portion of said originalsound current so as to obtain a differential sound current distortedreversely by the amount of said distortions, and recording said lastmentioned current.

'7. The method of making corrected records, that includes producing anelectrical sound current from the original sound, producing from aportion of said original sound current and by utilization of thedistorting characteristics of the sound reproduction system anelectrical current representing distortions of reproduction, oppositelycombining said distortion representing SOI current with another portionof said original sound current so as to obtain a differential soundcurrent distorted reversely by the amount of said distortions, andrecording said last mentioned current.

8. rhe method of making corrected sound records, that includes producingan electrical sound current from the original sound, producing from aportion of said original sound current and by utilization of thedistorting characteristics of the sound reproduction system anelectrical current representing distortions of recording andreproduction, oppositely combining said distortion representing currentWith another portion of said original sound current so as to obtain adifferential sound current distorted reversely by the amount of saiddistortions, and recording said last mentioned current.

9. A sound record modifying system, comprising means for producing anoriginal electrical sound current from an original sound, means fordistorting a portion of said sound current in accordance with thedistorting characteristics of a sound reproducing system, means fordiiTerentially combining said last mentioned distorted sound currentwith a portion of the original sound current, in such manner as toobtain an electrical sound current distorted reversely by the amount ofthe distortionsand means for recording said reversely distortedelectrical sound current.

10. A sound record modifying system, comprising means for producing anoriginal electrical sound current from an original sound, means foraudibly reproducing sound fed by said original sound current, means forproducing an electrical sound current from said reproduced sound, meansfor diierentially combining said last mentioned electrical sound currentwith a portion of said original sound current in such manner as toneutralize said currents with the exception of a resultant electricalcurrent representing distortions of reproducing and picking up thesound, means for negatively combining said distortion representingcurrent with a portion of said original current in such manner as toreversely distort said current, and means for recording said reverselydistorted current.

ROY J. POMEROY.

